Neuronal Communication✅ Flashcards
What pathway does a nervous response usually follow
Sensory receptor
Sensory neurone
Relay neurone
Motor neurone
Effector
What is the function of a sensory neurone
Transmits impulses from receptors to relay neurones in the central nervous system
What are the key structural features of a sensory neurone
One dendron (carrying impulse from receptor to cell body)
One axon (carrying impulse from cell body to a relay neurone)
What is the function of a relay neurone
Transmit impulses between neurones
What are the key structural features of a relay neurone
Many clusters of dendrites, each leading to a dendron.
Each dendron passes to central cell body
Short axon carries impulses from the cell body to many synaptic endings
What is the function of a motor neurone
Transmit impulses from a relay neurone to an effector (ie muscle or gland)
What are the key structural features of a motor neurone
Dendrites leading to the cell body. One long axon (carrying impulses from cell body to effector)
How do sensory and motor neurones look different
Sensory: cell body and nucleus in middle of dendron
Motor: cell body and nucleus left of dendron
What does a dendron, axon, dendrites, myelin sheath, nodes of ranvier, cell body and nucleus look like on a diagram of a neurone
Dendron: the start of the axon
Nucleus: small circle in cell body
Cell body: surrounds nucleus
Dendrites: little circles on end of
Myelin sheath: around the axon
Node of ranvier: gaps in myelin sheath
Axon: line connecting cell body away
What are myelin sheaths made from, what do they do
Fat produced by Schwann cells
Speed up nervous impulse by enabling saltatory conduction (axon membrane can depolarize only at nodes of ranvier, action potential jumps between nodes which is more efficient then entire membrane being depolarized
What do receptors do
Detect change in environment and convert stimulus into electrical impulse
What are the 5 types of stimulus
Pressure
Light
Chemicals
Temperature
Sound
What receptor and describe mechanistic detail for pressure stimulus
Receptor: pacinian corpuscle
Detail: pressure applied to skin opens stretch-mediated sodium ion channels, triggering an action potential
What receptor and describe mechanistic detail for light stimulus
Receptor: rods cells (in retina of eye)
Detail: light causes a chemical reaction to occur in rod cells (ie breakdown of rhodopsin), which alters the permeability of the cell membrane to sodium ions
What receptors and describe mechanistic detail for chemical stimulus
Receptors: taste receptor, olfactory cells
Detail: molecules or ions (eg salt, sugar, odour molecules) bind to receptors on the receptor cell membranes, this causes a second messenger response, cAMP levels rise and alter permeability of the cell membranes to Na+ ions. Depolarization occurs and triggers an action potential
What receptor and describe mechanistic detail for temperature stimulus
Receptor: thermoreceptors
Detail: specialized sensory neurones. The permeability of their membranes to Na+ ions changes with temperature
What receptor and describe mechanistic detail for sound stimulus
Receptor: hair cells (in the ear)
Detail: sound waves move cilia on hair cells, which triggers changes in membrane permeability to K+ ions
What is action potential
The change in potential difference across a neurone membrane following a stimulus (approx +40mV)
What is the resting potential in mV
-70mV
How does the sodium-potassium pump produce resting potential
3 Na+ ions pumped out of neurone (by active transport) for every 2 K+ ions pumped in. This sets up an imbalance of positive charge (ie outside the neurone is more positive then inside)
How do K+ channels produce resting potential
Some K+ channels remain open, this enables some K+ ions to diffuse out of neurone, down a concentration gradient. Even more positive charge therefore builds up outside of the neurone
What happens during an action potential
Resting potential
Na+ channels open. Na+ ions diffuse into neurone down an electrochemical gradient
Initial influx on Na+ ions causes more voltage gated Na+ channels to open (depolarization)
Na+ ions continue to diffuse into neurone through voltage gated Na+ channels until potential difference reaches +40mV. Voltage-gated Na+ channels then close and voltage-gated K+ channels open
K+ ions diffuse out of neurone, reducing the positive charge inside the neurone and repolarising the membrane
Voltage-gated K+ channels close. The membrane becomes hyper polarized (due to K+ ions leaving, inside becomes more negative then resting state). Known as refractory period- no more action potential occurs until resting potential restored. Na-K pumps return the neurone to resting potential
The propagation of an action potential involves what events
Na ions enter a neurone and depolarize it
Na ions diffuse further along the neurone
The increased positive charge caused by diffusion of Na ions open more voltage-gated sodium ion channels
Action potential passes along the neurone
What 3 factors affect the speed of nerve impulses
Greater axon diameter (reduced resistance to ion flow)
Higher temperature
Presence of myelin
Describe the transmission across a synapse
Action potential passes to end of presynaptic neurone (presynaptic knob)
Voltage-gated Ca2+ ion channels open
Ca2+ ion influx causes vesicles containing neurotransmitters (acetylcholine) to fuse with neurones cell membrane
Neurotransmitters (acetylcholine) released into synaptic cleft by exocytosis
Neurotransmitters (acetylcholine) diffuse across synaptic cleft and bind to receptors on postsynaptic neurones cell membrane
Na ion channels and triggered to open, causing depolarization and an action potential in postsyanptic neurone (if sufficient neurotransmitters bind and threshold value surpassed)
What are the roles of synapses
Ensure impulses travel in only 1 direction
1 presynaptic neurone can signal to many postsynaptic neurones, this enables signals to be passed to different effectors
Enable 1 sensory neurone to revive signals from several receptors, this provides information about extent of stimulus. Spatial summatation occurs- ie sometimes an action potential in a postsyanptic neurone will occur only if several presynaptic neurones release neurotransmitters
Enable temporal summation- ie sometimes a postsynaptic action potential occurs only when several impulses have travelled down a presynaptic neurone. Each impulse releases more neurotransmitters until threshold depolarization is surpassed in postsynaptic neurone
What is the central nervous system (what types of neurones)
Brain and spinal cord
Relay neurones
What is the peripheral nervous system (what type of neurones)
Everything other then brain and spinal chord
Sensory and motor neurones
What is the somatic nervous system
Conscious control input from sense organs output to skeletal muscles
What is the autonomic nervous system
Subconscious control input from internal receptors output to smooth muscles and glands
What is the sympathetic and parasympathetic motor systems
Sympathetic: fight or flight responses, neurotransmitters-noradrenaline
Parasympathetic: relaxing responses, neurotransmitter-acetylcholine
What is the function of the cerebrum where is it located
Coordinates voluntary responses
Top of the brain (a bit right)
What is the function of the cerebellum where is it located
Controls balance and posture
Weird looking tree bit bottom right of brain
What is the function of the medulla oblongata, where is it located
Autonomic functions (eg heart rate, breathing rate)
Bottom of brain (just left of spinal chord)
What is the function of the hypothalamus, where is it located
Autonomic functions (eg thermoregulation)
At the top of the medulla oblongata
What is the function of the pituitary gland where is it located
Release hormones that control other glands in the body
Left of hypothalamus
Describe the stimulus, receptor, location of relay neurone, effector and importance of the knee-jerk reflex
Stimulus: firm tap below kneecap
Receptor: stretch receptor in muscles
Location: spinal chord
Effector: muscles in upper leg
Importance: maintaining balance
Describe the stimulus, receptor, location of relay neurone, effector and importance for the blinking reflex
Stimulus: touch on cornea
Receptor: touch receptor in the cornea
Location: lower brain stem
Effector: muscles in eyelids
Importance: preventing damage to the eyes
Describe skeletal muscle
Appearance:Striated
Location:Attached to bones via tendons
Type of contraction:Voluntary (conscious), fast, short in duration
Describe cardiac muscle
Appearance: striated (fainter striations then skeletal)
Location: heart
Type of contraction: involuntary, intermediate speed, intermediate duration
Describe smooth muscle
Appearance: non-striated
Location: walls of blood vessels, digestive system, excretory system
Type of contraction: involuntary, slow, can be long-lasting
describe the role of cell signalling in the nervous system (2 marks)
transmits nervous impulses between neurones
across synapses/ synaptic clefts
for coordinated responses to stimuli
idea of summation
explain why homeostasis relies on cell signalling (2 marks)
receptor cells need to communicate with controller/coordinator/brain
controller/coordinator/brain needs to communicate with effectors
idea of several cell types/tissues/systems involved in responses
state the 2 structural differences between a sensory neurone and a motor neurone (2 marks)
position of cell body (described)
sensory neurones has one (long) dendron
motor neurones has many dendrites leading to its cell body
many relay neurones are not surrounded by myelin sheath, suggest why (2 marks)
relay neurones tend to be short
the increased rate of conduction in the presence of myelin sheath would make little difference
explain why sensory receptors are considered to be transducers (1 mark)
they convert one form of energy to another form of energy
state the form of energy converted to electrical impulses by
A: rod cells
B: thermoreceptors
C: Pacinian corpuscles
D: olfactory cells
A: light
B: heat/thermal
C: mechanical pressure
D: chemical
describe how the transmission of nerve impulses differs between myelinated and unmyelinated neurones (3 marks)
(with myelination)
faster impulses
saltatory conduction
longer local circuits
nodes of Ranvier present
explain why a neurone will not produce action potentials that vary in magnitude (3 marks)
all or nothing principle
threshold potential must be surpassed
no action potential will occur if Na+ ion influx is insufficient
stimulus strength does not affect action potential magnitude (above threshold)
K+ ion channels always open at the same point in an action potential (which results in the potential difference never surpassing a particular value)
describe how acetylcholine is released from a presynaptic neurone (3 marks)
calcium ion channels open/ calcium ions diffuse into presynaptic neurone
vesicles fuse with the presynaptic membrane
acetylcholine is released by exocytosis
use the concept of temporal summation to explain why a weak stimulus may be filtered out and not produce a response from the nervous system (3 marks)
a weak stimulus produces less frequent action potentials
fewer neurotransmitter molecules are released
less depolarisation (in post synaptic neurone)
threshold is not reached
no postsynaptic action potential
suggest why it is important for neurotransmitters such as acetylcholine to be recycled (2 marks)
to be released again from the presynaptic neurone
regulates the concentration of neurotransmitter in the synaptic cleft
prevents re-binding to receptors when signalling has stopped
which specific branch of the peripheral nervous system would produce the following responses
A: a person gripping a cup with their hand
B: an increase in sweat production
C: constriction of pupils (3 marks)
A: somatic
B: sympathetic
C: parasympathetic
explain why a person struggling to move normally may have suffered damage to either their cerebrum or cerebellum (2 marks)
the cerebrum controls voluntary movements
cerebellum coordinates balance and non-voluntary movements
state the location of the relay neurones in
A: knee-jerk reflex
B: the blinking reflex (2 marks)
A: spinal chord
B: brain stem
describe and explain the general characteristics of reflex responses that aid the survival of organisms (4 marks)
few synapses
short pathway
a dangerous stimulus is responded to quickly
innate/ no learning required
the response is stereotyped/consistent/always the same
involuntary
prevents overloading of the brain
explain how the typical neural pathway of a reflex maximises its effectiveness (3 marks)
2 synapses
short relay neurone
sensory neurone does not need to travel deep into the brain
responses is quicker
how will the length of the following sarcomere features change during muscle contraction (5 marks)
A: A band
B: I band
C: myosin filaments
D: actin filaments
E: H zone
A: no change
B: shortens
C: no change
D: no change
E: shortens
outline the role of calcium ions in muscle contraction (3 marks)
calcium ions bind to troponin
changes the shape of troponin
displaces tropomyosin
uncovers myosin binding sites on actin
enables myosin heads to bind to actin
